Hydrocarbons (HCs) are environmentally friendly natural refrigerants and are expected to be promising alternative candidates to replace some currently used halogenated hydrocarbon refrigerants. Some available data sets for HCs used to formulate the equations of state (EoS) for them are relatively old, so we point out that new data with less uncertainty are expected to play an essential role in updating the EoS for HCs. Therefore, a set of PVT property measurements for hydrocarbon refrigerants including propane, n-butane, and isobutane was conducted in the present study. A newly developed vibrating-tube densimeter was employed for the measurements, and then a total of 430 liquid PVT properties were obtained, including those at the saturation boundaries. The measurement range is (240 to 380) K for temperature and up to 7 MPa for pressure. The measurement uncertainty is about 3 mK for temperature, 0.26 kPa + 0.022% for pressure, and 0.1 kg‚m -3 + 0.024% for density. The present data were compared with available thermodynamic models that are currently considered to be the most reliable. A set of modified Tait equations of state for the liquid phase are also discussed.

The isobaric ideal-gas heat capacity for HFO-1234yf, which is expected to be one of the best alternative refrigerants for HFC-134a, was determined on the basis of speed-of-sound measurements in the gaseous phase. The speed of sound was measured by means of the acoustic resonance method using a spherical cavity. The resonance frequency in the spherical cavity containing the sample gas was measured to determine the speed of sound. After correcting for some effects such as the thermal boundary layer and deformation of the cavity on the resonance frequency, the speed of sound was obtained with a relative uncertainty of 0.01 %. Using the measured speed-of-sound data, the acoustic-virial equation was formulated and the isobaric ideal-gas heat capacity was determined with a relative uncertainty of 0.1 %. A temperature correlation function of the isobaric ideal-gas heat capacity for HFO-1234yf was also developed.

Concerning an increasing demand for environmentally friendly refrigerants including hydrocarbons, thermodynamic properties of such new refrigerants, especially densities, are essential information for refrigeration engineering. A rapid density-measurement system with vibrating-tube densimeter was developed in the present study with an aim to supply large numbers of high-quality PVT property data in a short period. The present system needs only a few minutes to obtain a single datum, and requires less than 20 cm3 sample fluid. PVT properties in the entire fluid-phase, vapor-pressures, saturated-liquid densities for pure fluid are available. Liquid densities, bubble-point pressures and saturated-liquid densities for mixture can be obtained. The measurement range is from 240 to 380 K for temperature and up to 7 MPa for pressure. By employing a new calibration function, density can be precisely obtained even at lower densities. The densimeter is calibrated with pure water and iso-octane which is one of the density-standard fluids, and then measurement uncertainty was evaluated to be 0.1 kg m−3 or 0.024% whichever greater in density, 0.26 kPa or 0.022% whichever greater in pressure and 3 mK for temperature, respectively. The performance of the present measurement system was examined by measuring thermodynamic properties for refrigerant R134a. The experimental results were compared with available equation of state and confirmed to agree with it within ±0.05% for liquid densities while ±0.5% in pressure for the gas phase.

In some refrigeration-based applications, hydrocarbons (HCs) are expected to be promising long-term alternative refrigerants because of their zero ozone depletion potential (ODP) and negligible global warming potential (GWP) values. But there exists a serious disadvantage that they are flammable. Despite their flammability, however, commercial demands for HCs are increasing not only in several European countries but also in southeast Asia. On the other hand, the flammability is considered a major issue in U.S.A. and Japan. To suppress the flammability, blended mixtures of HCs with nonflammable HFCs are considered. As one of such mixtures, pentafluoroethane (R-125) and propane (R-290) mixtures are dealt with in the present study. Although the thermodynamic properties of each single component have been studied rather extensively, there is no study reported on those of this binary system. Accordingly, we have measured the gas-phase P ρ Tx properties of the binary R-125 (1) + R-290 (2) system by using the Burnett isothermal−isochoric coupling method. The present measurements cover an extensive range of temperatures (305 to 380 K), pressures up to 4.5 MPa, and densities up to 2.5 mol·dm-3 for the binary systems with four different mole fractions of x 1 = 0.00, 0.29, 0.50, and 0.75, respectively. The present paper discusses the gas-phase P ρ Tx properties for the first time regarding the present binary mixtures at their selected compositions.

Experimental thermodynamic property data for hydrocarbon refrigerant mixtures are more important now in order to improve the performance of existing equations of state. In the present paper, liquid-phase PVTx data including bubble points for the binary and ternary systems composed of propane (1), n-butane (2), and isobutane (3) are reported. More than 1000 measurements were made by employing a newly developed vibrating-tube densimeter system with an uncertainty of 0.1 kg·m-3 + 0.024% for density, (3 to 7) mK for temperature, 0.26 kPa + 0.022% for pressure, and 0.1 mol % for composition. The present data contain the first set of experimental PVTx data for the ternary system. The measured data are compared with two available thermodynamic mixture models developed by Lemmon and Jacobsen and Miyamoto and Watanabe. A mixture model applied for a modified Tait equation of state is also presented in this paper.